Piston



M. B. COVERT PISTON Filed Feb. '7l 1921 i Patented Aug. 11, 1931 aus? MARTIN B. COVERT, OF INDQEANAE'QLIS, INDIANA, ASSIGNOR, BY NESNE ASSIGNMENTS, T THE CLEVELAND TRUST COMPANY, F CLEVEILAND, OHIO, A CORPMTION 0F @HEC Application led February '.A?, 192i.

This invention relates to istons or internal combustion engines. t 1s especially concerned with pistons composed of a material the coeiicient of expansion of which 5 is greater than that of the material composing the walls ,of the engine cylinder.

@ne object of the invention is to provide a piston capable of operation in an engine cylinder at various temperatures wit a i@ very small initial clearance.

Another object is to provide an aluminum alloy piston capable of operating in an iron cylinder at various temperatures with a very small initial clearance.

Another object is to provide an internal combustion engine piston having substantially constant maximum diameter across the thrust aces of the skirt at all temperatures.

Another object is to provide an internal combustion engine piston 'adapted to maintain a uniform clearancebetween the thrust iaces of the skirt and the engine cylinder walls at all temperatures.

Another object of the invention is to provide a piston having a skirt adapted automatically to adjust its shape and size to the confining cylinder walls.

Other objects will be pointed out in the following speciiication in which my invention is set forth.

Many efforts have Abeen made to design pistons for internal combustion engines which could be itted into the engine cylinder with a relatively small clearance or space between the wallspf the piston and cylinder at ordinary temperatures and which would not seine or stick in the i cylinder when they became highlv heated. When the materials composing the piston and cylinder have substantially the same coeliicients of expansion it is not extremely difiicult to realize these aims in part, although in use the piston becomes more highly heated than the cylinder, since the latter is artificially cooled b v water jackets, heat radiating fins, etc. There are. limits of clearance, however, below which-pistons will seize in cylindersof the same material. For D instance iron pistons fitted into iron cylincylinder durin Serial No. 442,989.

ders with a very small clearance, say .002 in a 3 piston will seize in the cylinder when heated.

iVhen aluminum pistons are used in an iron cylinder, much more difficulty is eX- perienced since the coeiiicient of expansion of aluminum is approximately three times as reat as that of cast iron. l

n order that pistons having hik h coefficients vof expansion., as compare with iron, may have ample clearance in an iron cylinder when heated and in use it is necessary to provide them with excessive clearance when cold. vThis large clearance permits lateral movement of the piston in the cylinder when the engine is first started producing noises, commonly known as slap or lincoln Variousexpedients have been resorted to in an effort to overcome these difficulties, but

so far as l am aware, up to this time no satisfactor solution has been found. By In invention, however, l provide a piston w ich is capable or" operating in an engine cylinder at all working temperatures with a very small initial clearance, regardless of the temperatures of the piston and cylinder and also regardless of the coefficients of expansiorn of the materials comprising` the piston and the cylinder. Furthermore, the piston'is automatic in adjusting itself to the changes incident to temperatures, spee s, rates and amounts of eX- pansion, etc., thereby maintaining substantially the same clearance between the thrust faces of the piston and the cylinder walls at all times.

One embodiment of my invention is disclosed in the drawings attached to this specification and forming a part hereof, in which;

Fig. l is a side elevation of a piston mounted in an internal combustion engine cylinder.

Fig. 2 is a sectional view taken on line 2--2 of Fig. l looking in the directions indicated and showing the clearance at the sides of the piston greatly exaggerated.

Fig. 3 is a cross sectional vlew taken on 'line 3-3 of Fig. 2 and;

may be integral with or otherwise suitably secured to the head 21" In the modification shown the two parts are integral and/comprise a piston of the general trunk type 1n which the skirt is a continuous substantially circular shell. The ordinary bosses 301 are inte ral with the inner surface of the skirt an are attached to and supported from the head 2 by a web 3b which also serves to connect the head and skirt and to make them function as a rigid nntary structure. Horizontal slots 4 cut entirely through the skirt 3 at its upperl end completely separate portions of the skirt from the ring flange of the head. These slots are preferably formed in diametricallyopposite sides of the skirt and are symmetrical with respect to a line drawn at ri ht angles to` the center line of the bosses. bviously the length. of the slots may vary but a minimum of and a maximum of 90@ has been found satisfacto elief ducts 5 suitably spaced in the skirt 3 permit the escape of oil from the cylinder walls to the interior of the\piston while ducts 6 conduct oil from the interior of the piston to the bosses4 and wrist pin.

The outer surface of the skirt is substantially cylindrical throughout its length but has diametrically opposite parts 7 which are slightly relieved or depressed below the true cylindrical contour thereof thus making the outer surface slightiy oval when the skirt is viewed in cross section. These relieved surfaces 7 preferably extend for about 60 en either side of the center o-f each lboss and join the two remaining surfaces 8 which constitute parts of the true cylindrical surface of the piston.

Since the surfaces 8 are located on a line drawn at right angles te thecenter line ef the bosses they constitute the thrust faces of the piston, namely those faces which takebthe lateralpressure of the piston caused by the angularity of the connecting rod with respect to the piston. These surfacesv ex,- tend for the full length of the skirt and,

being formed with a radius of curvature substantially the same as that'of the inner surface of the cylinder in which the piston 10 and llindicate respectivelv a wrist pin and connecting rod, the former bein mounted in` the bosses 3m with an easy s ding t when cold so as not to hinder expansion and contraction of the skirt and being retained in position in the bosses by spring rin s l5 or otherwise.

n practise the piston here disclosed may be made by suitably machining an ordinary trunk type piston. After the outer. surface of the skirt has been made substantially cylindrical and of a diameter only very slight less than that of the cylinder in which the piston 1s to operate, the surfaces on the sides' I adjacent the bosses are relieved to form surfaces 7. This may be done by.a turning operation the piston being mounted slightly off center for each surface with the result that the surfaces 7 are then eccentric with regpnnt fn flan infmr Qur-Farm nf filmx Qlrirf. und

the skirt wall is thinnest at the center line thru the bosses and of uniformly varying time the piston is being cast as is well known in the art., When the slots are to be sawed or similarly formed in the piston the operation of forming them may advantageously be performed after the piston has been more or Aless completely Jmachined. L L L .Diameter of cylinder, 3.500; diameter of piston across surfaces 8,- 3.498"3.499 diameter of piston across surfaces 7, 3.4803.485.

It is diicult to determine the exact manner in which the. various parts of this piston perform but my theory of their operation is as follows: The head 2 expands radially outward in all directions when the piston becomes heated. As its diameter increases it carries radially outward with it the por tions of the skirt 3 to which it is connected, namely the longitudinal wall portion 12 adjacent the bosses, this outward movement ybeing permitted in the cylinder by the space or clearance between thecylinder Wall and the surfaces 7 of the iston. The thrust face wall portions 13, owever, being separated .from the head, are not carried radially outward when the head expands. Probae only increase in the. diameter of these wall portions is due to the expansion miese? or .the srt as a whole, as its tem erature increases by the transfer of heat rom the head 2 and cylinder to skirt 3. rlhe outward movement of the wall ortions 12 in conjunction with the head is resisted by the thicker wall portions 13, but when the connections between the head and these portions are suliciently rigid the oitions l2 will be distorted circumferentia ly and the portions 13 will move inwardly substantially without distortion ythus preserving at all times their large bearing surface for contact with the cylinder walls. This distortion of the skirt brings the surfaces 7 int-o increasingly closer Contact with the cylinder walls as the temperature of the piston is raised while, coincident therewith, the surfaces 8 tend to recede from the cylinder walls.

lt will be noted that l have provided a piston the skirt of which is adapted to permit expansion thereof at a faster rate and to a greater amount than that of the cylinder without undue decrease in the clearance between the parts of the piston which are initially in close contact with the cylinder wall.

lt will further be noted that l have provided a design of piston especially suited to aluminum alloys since the diderence iii the coeficiente of expansion of the aluminum piston and the iron cylinderare taken care of without noticeable decrease in the amount oit' clearance between the thrust faces of the piston and the cylinder.

lt will also be noted that l have provided a piston which may be iitted into the cylfinder` so closely that no disagreeable slapping or knocking noises will take place at ordinary temperatures and that all danger ci seizure is avoided when heated.

Altho ll have described-one modiyicaticn ci my invention in detail l have done so merely :for the purpose of illustration and not with the desire to be limited thereto,

'since it is obvious that many variations in the modilication described could be made by those skilled in the art without departing from the scope of my invention. l wish to be limited only by what is claimed.

What is claimed:

l. ln an internal combustion engine piston a circular head disc having a ring lian e depending therefrom and a substantiall cylindrical skirt the said skirt having longitudinal portions of di'erent thicknesses, the

said head being connected to the thinnerl longitudinal portions and separated from the thicker longitudinal portions by narrow air gaps of greater circumferential length than the said thicker portions, the thinner portions being relieved exteriorly throughout their entire length, and a rib extending across the said head disc and integral with the said head and thinner skirt portions.

2. In a iston for an internal combustion engine, a ead comprising a circular disc with a ring flange de ending :fromthe periphery thereof, a s irt having opposite, longitudinally extending bearing wall portions and other opposite longitudinally extending boss carrying wall portions having their outer surfaces relieved throughout substantially the entire length thereof, and being thinner than the said bearing wall portions, the said boss carrying wall portions being integrally connected to the head, and a rib extending across the head disc and formed integrally with the said disc and boss carrying wall portions.

3. ln a piston for an internal combustion engine a head comprising a circular disc and a depending ring i'iange, a skirt having longitudinally extending relatively rigid portions separated from the said head and other longitudinally extending relatively distortable portions having their -outer surfaces relieved throughout their length and secured to the head, and reinforcing means extending across the said head disc and longitudinally of' the said distortable portions.

4l. A hollow piston for internal* combustion engines including a head and a body integral therewith and formed from a metal lighter than iron, said body being non-compressible circumlierentially and having internal aligned wrist pin bosses and also having external bearing areas of considerably less than 90 degrees lcurvature located between said bosses, the head portion having a plurality or1 piston ring grooves and the piston having transverse slots between said bosses and lon the side oli said grooves nearest said bosses and separating part of the head from said bearing areas, the head having an internal rib extending across from one et said bosses to the other, the piston being externally relieved except for said bearing areas, whereby heat from the head is conducted rapidly to said bosses.

5. A piston for an internal combustion engine comprising a head having a depending ring flange, a skirt relieved on opposite sides thereof and a rigid connection between the relieved sides 'of the skirt and the said piston head, the piston being adapted aiitoniatically to maintain the maximum initial diameter across the thrust faces of the skirt y substantially constant at various temperatures.

6. A piston for an internal combustion engine comprising a head disc and integral rin ange a skirt exteriorly relieved on opposite sides thereof and a rigid connection between the said relieved sides of .the skirt and the head, the maximum initial diameter out their entire length.

portions.

tially constant, under varyin voperating conditions, the initial difference tween the.

maximum diameteracress the thrust faces of the skirt and the inside diameter of' the cylinderl in which it operates. y

7. In an internal combustion engine piston a circuar head disc having a rmg ange depending therefrom and a substantlallyr cylindrical skirt the said skirt having lon 1 tudinal portions of dierent thicknesses, t

said head being connected tothe thinnerv longitudinal portions and separated from the thicker longitudinal portions by narrow air gaps of greater circumferential length than the said thicker ortions, the thinner portions being relieved) 8. In a piston for an internal combustion engine a head comprising a circular disc and a depending ring a'nge, a skirt having longitudinally extending relatively rigid portions separated from the said head and other longitudinally7 extending relatively distortable portions having their outer surfaces relieved throughout their length and secured to the head, and reinforcing meansextending longitudinally of the same 9. In an lnternal'combustion engine piston, a head and a continuous skirt that is noncompressible circumferentially havingintegrallyV connected longitudinal ortions of Vdifferent thicknesses, said head belng connected to the thinner longitudinal portions and separated from the thicker longitudinal portions by narrow air gaps, the thinner portions being exteriorly relieved throughout their entire length, and reinforcing ribs integral with the head and extending longitudinally vofthe thinner skirt portions.

10. A piston for an internal combustion engine comprising a head, a skirt relieved 'on opposite sides thereof and provided with opposed integral wrist pin bosses and a rigid connection between the opposite relieved sides of the skirt including a rib member that connects each wrist pin boss with a substantial part of the head, the piston being adapted automatically to maintain the maximum initial diameter across the thrust faces of the skirtsubstantially constant at various temperatures,

In testimony whereof, I hereunto aix my signature.

MARTIN B. CVER'I.

exteriorly throughdistortable 

